Most of conventional communication apparatus are designed to have a main battery and a sub battery. In such communication apparatus, main operations of the communication apparatus is performed by the main battery, and operations of maintaining a memory, clocking time and the like are performed by the sub battery when the main battery of the communication apparatus is not operated. Since the communication apparatus is provided with plural batteries as described above, a clock can be operated by the sub battery even when the main battery is removed, therefore, the current time can be kept accurate.
However, to provide plural batteries on the communication apparatus increases size and weight of the device, further, requiring costs for mounting these batteries, therefore, it is preferable in some cases that only the main battery is mounted as the power supply source on the communication apparatus which is taken along as a mobile unit. For example, in JP-A-2004-15713, there is disclosed a communication apparatus which can correct time at any time by housing a radio controlled clock. In this communication apparatus, it is not necessary to mount a secondary battery by housing the radio controlled clock.